1. Field of the Invention
The present invention generally relates to electronic component value trimming systems and particularly relates to a system for trimming the effective value of an electronic component such as a resistor in an integrated circuit (IC) to a desired value.
2. Description of the Related Art
Conventional techniques for trimming the effective value of an electronic component to a desired or target value comprise selectively connecting a main component to one or more trimming components via a network of switchable interconnections. Such systems can compensate for the tolerance of IC components such as resistors and provide a more accurate value than possible with an uncompensated component. There are applications where well controlled IC resistor networks are desirable. One such application, for example, is in the termination of transmission lines to optimise signal quality.
Many conventional systems have the disadvantage of static power consumption. This can be particularly problematical in low power applications. In addition, where such systems involve the distribution of an analogue voltage signal, there can be susceptibility to interference and error. Conventionally, these problems have been addressed by digital systems at the expense of increased complexity and increased silicon real estate.
An example of a conventional trimming system is described in U.S. Pat. No. 5,134,311. Here, the output impedance of a voltage driver is adjustable. Multiple parallel pull up and pull down transistors are located in the output of the driver. The output impedance of the driver is selected by activating a corresponding group of the transistors.
Another example of a conventional trimming system is described in U.S. Pat. No. 6,026,456. Here, a termination network for optimising a bus impedance is described. The network has a higher impedance than the bus impedance to be controlled.
Yet another example of a conventional trimming system is described in U.S. Pat. No. 5,652,538. Here, there is described a digital system in which parallel elemental conductances are switched in and out of circuit by a digital control signal to obtain a desired impedance. In this design, there is also significant overhead in the system control logic. This overhead is a disadvantage for applications in which there are multiple components to be trimmed on an IC. Either the control logic has to be replicated to trim individual or groups of components, or the control logic has to trim all components centrally. The latter may involve complex routing of a control bus across the IC. The control bus may have many bits, further complicating such routing.
It would therefore be desirable to provide a component value trimming system for IC applications in which the aforementioned problems associated with conventional systems are alleviated.